<template>
  <!-- 返回顶部 -->
  <transition :name="transitionName">
    <div v-show="visible" :style="customStyle" class="back-to-ceiling" @click="backToTop">
      <svg
        width="16"
        height="16"
        viewBox="0 0 17 17"
        xmlns="http://www.w3.org/2000/svg"
        class="Icon Icon--backToTopArrow"
        aria-hidden="true"
        style="width: 16px; height: 16px"
      >
        <path
          d="M12.036 15.59a1 1 0 0 1-.997.995H5.032a.996.996 0 0 1-.997-.996V8.584H1.03c-1.1 0-1.36-.633-.578-1.416L7.33.29a1.003 1.003 0 0 1 1.412 0l6.878 6.88c.782.78.523 1.415-.58 1.415h-3.004v7.004z"
        />
      </svg>
    </div>
  </transition>
</template>
<script setup lang="ts" name="BackToTop">
import { CSSProperties } from 'vue';

export interface BackToTopProps {
  visibilityHeight?: number;
  backPosition?: number;
  customStyle?: CSSProperties;
  transitionName?: string;
}

// 接受父组件参数，配置默认值
const props = withDefaults(defineProps<BackToTopProps>(), {
  visibilityHeight: 400,
  backPosition: 0,
  customStyle: () => {
    return {
      right: '50px',
      bottom: '50px',
      width: '40px',
      height: '40px',
      'border-radius': '4px',
      'line-height': '45px',
      background: '#e7eaf1'
    };
  },
  transitionName: 'fade'
});

let visible = ref(false);
let interval = ref();
let isMoving = ref(false);

onMounted(() => {
  window.addEventListener('scroll', handleScroll);
});

onBeforeUnmount(() => {
  window.removeEventListener('scroll', handleScroll);
  if (interval.value) {
    clearInterval(interval.value);
  }
});

const handleScroll = () => {
  visible.value = window.pageYOffset > props.visibilityHeight;
};

const backToTop = () => {
  if (isMoving.value) return;
  const start = window.pageYOffset;
  let i = 0;
  isMoving.value = true;
  interval.value = setInterval(() => {
    const next = Math.floor(easeInOutQuad(10 * i, start, -start, 500));
    if (next <= props.backPosition) {
      window.scrollTo(0, props.backPosition);
      clearInterval(interval.value);
      isMoving.value = false;
    } else {
      window.scrollTo(0, next);
    }
    i++;
  }, 16.7);
};
const easeInOutQuad = (t: number, b: number, c: number, d: number) => {
  if ((t /= d / 2) < 1) return (c / 2) * t * t + b;
  return (-c / 2) * (--t * (t - 2) - 1) + b;
};
</script>

<style scoped>
.back-to-ceiling {
  position: fixed;
  z-index: 99;
  display: inline-block;
  text-align: center;
  cursor: pointer;
}
.back-to-ceiling:hover {
  background: #d5dbe7;
}
.fade-enter-active,
.fade-leave-active {
  transition: opacity 0.5s;
}
.fade-enter,
.fade-leave-to {
  opacity: 0;
}
.back-to-ceiling .Icon {
  background: none;
  fill: #9aaabf;
}
</style>
